THE DISH
THE DISH
This is the most visible component, a parabolic reflector which
may consist of Solid Aluminum, Perforated Aluminum, Fiberglas
or wire-mesh. Dish sizes vary from small .5-2m for the Ku band
and all the way to 3.7m to 6m for C band reception, the 3m ORBITRON SX-10 being
most common - for weak transponders a ORBITRON SX-12 with MicroMesh
is the best choice. The dish/antenna is the device that focuses
the microwave signals coming from the satellites much as the mirror
in a reflecting telescope concentrates the light from distant
galaxies.
THE MOUNT
The most common type of dish mount is called a Polar Mount,
so named because it is oriented to coincide with the earth's axis,
enabling it to "track" the satellites, which are spread
out in Geostationary orbit in a band of the sky called the "Clarke
Belt", named after Arthur C. Clarke, who conceived the concept
of Geostationary communications satellites back in 1945.
Most (but not all) mounts are sunk in concrete and require a 3.5" OD pole of schedule
80 steam pipe or used "drill stem". In many areas, this
is available from salvage dealers at very reasonable prices or
Steel & Tube Ltd. ( OD refers to outer diameter)
THE POSITIONER ARM (Actuator)
A device containing a motor that is used to swing the satellite
dish to allow it to focus on individual satellites, which may
be as close to one another as 2 degrees of arc. Actuator arms
are most commonly found in 18- and 24-inch lengths (the longer
the arm, the wider the arc that the dish can "see".)
In addition, a more expensive aiming mechanism, called a "horizon-to-horizon"
mount, is capable of more precise aiming (important on Ku band
and closely-spaced satellites), as well as being able to see the
entire satellite arc (from your Western horizon through North and then to your Eastern horizon) from your location given no physical obstructions
between the dish and the satellite. Many true dish heads have
also added a second actuator to control the vertical aspect (elevation)
of the dish, to enable them to track inclined orbit satellites
which "wobble" or vary in the vertical plane.
THE LNB
This is the Little high tech electronic gizmo that amplifies the very weak signals
from the dish, and also converts them to a more suitable band
of frequencies. LNB means Low Noise Block-converter. Older systems
consisted of separate components: LNA (Low Noise Amplifier) and
a downconvertor which changed the received signals (3-4 gHz, or
GIGAherz ....A GIGAHerz is one thousand megaHz....) to 70Mhz.
In the current range of LNB's the output for both C and Ku bands
is a 950 to 1450 Mhz block frequencies referred to as the IF frequency. There is also a device called
an LNBF, which combines the LNB and Feed Horn into a single unit.
(See below for description of feed assembly. The LNBF device uses
a simpler method for adjusting the polarity (voltage right on
the LNB cable - 14v tells the LNBF to receive Vertical transponders while 18v selects Horizontal transponders). You can not adjust fine skew, just H or V.
An LNBF is especially suitable for dedicated operations, such as a smaller
dish used for only one satellite - like the proposed NZ SKY Satellite service.
THE FEED HORN ASSEMBLY
The feedhorn acts as a microwave "funnel". This device
places the LNB at the focus of the dish, and is usually just called
"the feed". There are several different types of feeds.
Single C band feed: Contains a mounting port for ONE C band LNB.
A device called a is located inside, which allows the reception
of both vertically polarised and horizontally polarised channels.
In general practice, the even channels are on the Vertical polarity
while the odd channels are on the opposite polarity. The actual
polarity scheme depends on the satellite in question. A Dual C band
feed allows the use of Two C band LNB's one for horizontal
polarisation and one for vertical. Dual Band Feed (C and KU):
has ports for two separate LNB's, one for C band and one for Ku
band. The most popular Dual Band feed
horns are the Chaparral Co-Rotor II+ and ADL. While these are
actually a compromise system, with some minor losses, but in practice
they work pretty well.
SATELLITE CABLES
This is a bundle of various wires and cables that run from
the dish to the receiver, and consist of cables for the C and/or
Ku LNB's, Power to the LNB (Usually 18vDC & sent over the
same coaxial cable) as well as power (36vDC) for the Positioner
arm, return signals for position readout, and control voltage
for the Polarotor. To operate the Actuator Arm requires two conductors
which are very thick to carry the 2+ amps required to power the
actuator arm to move your dish) and two or three smaller cables
for the return data (pulses) for position readout from actuator.
The position readout cable from the actuator to the actuator controller
may have THREE conductors for the position sensor. For pot sensors,
one is for the tap, the other two are for the resistor. For pulse
sensors, one is ground, one is +5V, and the other is pulse input
- for "hall effect" sensors only two cables are required.
The most popular actuators on the NZ market (VonWeise) use two
cables for the position readout data. Polarotors use a three wire
connection. One for +5V, one for ground, and one for "pulse".
RG-6u Coax cable (rather than the often-seen RG-59U) is the cable
of choice for the higher frequencies of satellite
TV. RECEIVER
There are many receivers available by a number of manufacturers, both new and used. The receiver takes the signal from the LNB and produces a TV picture from the wideband FM video, and also allows you to tune subcarrier audio, which can provide many different audio only services such as music and talk shows. Newer receivers work with the standard 950-2045 mhz block that comes out of a standard LNB.
DECODER
The de-facto digital decoder in the South Pacific is the Scientific
Atlanta MPEG-2 DVB complaint decoder called the D9223, their are
some services using the Scientific Atlanta B-MAC decoders but
these will lightly up grade to the Scientific Atlanta PowerVu
digital system.. All decoders must be authorised by the programmer
and in most cases a annual subscription fee paid. We carry
the BENJAMIN DB-6000 which is suitable for receiving "Free-to-Air" TV & Radio services.
The DigiSkan ST888 is specially designed for receiving the European Bouquet for AsiaSat-2.
IS THERE A GOOD CHEAP BOOK THAT WILL HELP ME UNDERSTAND SATELLITE
TV FURTHER?
Space Pacific Ltd publish a book written by Bob Cooper called
"All You Need to Know about Satellite Television" which
is available from Telsat Communication Ltd at NZ$12.00 include
postage & GST (NZ only) We also have Mark Long's latest edition of Satellites in Asia/Pacific
book. A new book to the scene is a publication from Gary Cratt
entitled "The Practical Guide to Satellite TV" - this focuses on the Pacific Region incl Australia and New Zealand - a very informitive book.
What SATELLITES Broadcast Television Programming to the Pacific Region?
The number of Satellite which you will be able to receive TV programming from will depend on where you live, what size dish you have, and
how low you can "aim" your dish to the horizon - the the case of NZ to the Western horizon. Playing
with the Intelsats, PanAmSat - PAS-2, AsiaSat-2-AS2, Palapa C2M and
the Russian Statsionar/Rimsat Satellites is common practice for
enthusiasts in NZ & the Pacific Islands. With the average
3m to 3.7m dish you may do just fine. To receive the signals,
you will need a circular feed, as unlike Domestic Palapa/Asiasat-2
birds that are Horizontally or Vertically polarised - i.e. Linear, International
satellites (Rimsat/Intelsat) use Right Hand, or Left Hand Circular
Polarisation. If you have a monster dish (16ft or more), you can possibily get by without
the proper feed, but you will loose at least 1dB of signal. Chaparral
makes a special feed for international satellites, at a cost of
around NZ$325 called a Corotor II+ International. As an alternative,
there is a dielectric insert you can obtain that will convert your
linear feed to circular. This component is quite cheap, about $20. You
will also need a multi-standard TV, or some means of viewing NTSC
and SECAM signals, which are different from the PAL system used
in the NZ. If you don't mind black and white, though, a B&W
TV is easily adjusted to pick up the TV broadcasts from USA, and is suitable for
the experimenter and tinkerer. Telsat can offer a cost effective
digital standards converter - the CYPRESS CDM-600, which will allow you not only to
view these international channels, but also to record them (you
can not use your standard PAL VCR to record NTSC or SECAM signals). Much
of the international TV traffic is on the Intelsat Satellites
located at 173,177,180 & 184 degrees East.
What Television Programming can I view?
From AsiaSat-2, Palapa C2M, PanAmSat-2 and three Intelsat Satellite there is a wide range of TV and Radio Programming available for viewing in the south Pacific region.
CNN, BBC & NHK(Japanese) all offer 24hr News programming. Sport programming is available from the new Sports channel broadcasting from Nauru called the "Pacific Sports Network" (PSN).
Various foreign language programming is available including up to 14 Chinese channels, French, Italian, German, Thai, Russian, Portuguese, Indonesian, Malaysian & Spanish TV channels.
Other TV programming includes Country Music TV, Eternal Word TV(Catholic), Bloomberg TV, National Geographics, CNBC etc.
Additionally many Radio services can be received from satellites.
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